1. Field of the Invention
The present invention relates to a display device with coordinate input function by which a man-machine interface is achieved between an electronic computer and its operator.
2. Description of the Prior Art
In the prior art, a liquid crystal display with coordinate input function is disclosed, for example, in Japanese patent application laid-open No 262835/1986 or Japanese patent application laid-open No. 81521/1988.
FIG. 1 is a constitution diagram of a display device with a coordinate input function in an example of the prior art. Also FIG. 2 is a sectional view of a liquid crystal display cell.
In FIGS. 1 and 2, reference numeral 1 designates a liquid crystal display cell where a liquid crystal 10 is sealed between two glass substrates 12, 13, numerals 2 and 3 designate transparent electrodes arranged at a predetermined distance on the glass substrates 12, 13, numerals 4 and 5 designate drive circuits to activate the transparent electrodes 2, 3, numeral 6 designates a control circuit, numeral 7 designates a magnetic field sensor, numeral 8 designates an amplifier to amplify output signals of the magnetic field sensor 7, numeral 11 designates a seal substance to seal the liquid crystal 10 between the glass substrates 12, 13, and numerals 14 and 15 designate polarizing plates.
Next, the operation of this arrangement will be described.
The control circuit 6 supplies an AC signal as a coordinate input detection signal in time sharing with a display drive signal through the drive circuits 4, 5 in sequence to the transparent electrodes 2, 3 arranged on the glass substrates 12, 13 of the liquid crystal display cell 1. As a result, a rotating magnetic field is generated on the periphery of each of the transparent electrodes 2, 3 by the coordinate input detection signal current. If the sensor 7 with a material having electromagnetic induction effect characteristics embedded therein comes close to the field, a detection voltage corresponding to the rotating magnetic field is obtained from the sensor 7. The detection voltage is amplified by the amplifier 8 to a suitable amplitude and then compared in sequence in synchronism with timing of the coordinate input detection signal applied to the transparent electrodes 2, 3, thereby an intersection position of the transparent electrodes 2 and 3 can be detected.
The display device with a coordinate input function of the above-mentioned constitution is advantageous in that display of the image and the coordinate input can be realized by the same transparent electrodes 2, 3 and a special coordinate input panel is not required.
Since the display device with coordinate input function in the prior art is constituted as above described and the coordinate input detection signal current flows through the transparent electrodes, basically, the transparent electrodes 2, 3 must not have a non-conductive part there along. However, liquid crystal display devices in recent years are called upon to have higher resolution, and in order to prevent deterioration in the contrast ratio of the display image, a liquid crystal display panel having a display screen divided into two, upper and lower, separately driven parts is used. Liquid crystal display panels are being significantly advanced, and a liquid crystal display panel of two-layer type to enable the black-and-white display is put to practical use in recent years and also a color liquid crystal display panel in combination of the liquid crystal display panel of two-layer type with a color filter has been developed.
FIG. 3 is a sectional view of a standard liquid crystal display panel of two-layer type in the prior art, and FIG. 4 is a constitution diagram of a liquid crystal display panel divided into two, upper and lower parts in the prior art. In FIGS. 3 and 4, reference numeral 1 designates a liquid crystal display cell, numerals 2U, 2L and 3 designate transparent electrodes, numerals 4U, 4L and 5 designate drive circuits, numeral 6 designates a control circuit, and numeral 21 designates a liquid crystal cell for phase compensation, which is constituted by sealing a liquid crystal 10 between glass substrates 32 and 33 with a seal substance 31 and compensates optical characteristics of the liquid crystal display panel 1. Since details of the principle or the like of the liquid crystal panel of two-layer type shown in FIG. 3 do not have direct relation to the invention, the description shall be omitted here.
As clearly seen from FIG. 4, each of the transparent electrodes arranged in the vertical direction is divided into an upper transparent electrode 2U and a lower transparent electrode 2L corresponding to the dividing of the display screen. In this case, the bottom end of the upper transparent electrode 2U and the top end of the lower transparent electrode 2L are within the liquid crystal display cell 1 and therefore cannot be drawn as electrodes outside the liquid crystal cell 1. Accordingly, the coordinate input detection signal current cannot flow through the transparent electrodes 2U, 2L, and the display device with coordinate input function as shown in FIG. 1 cannot be constituted as in the prior art.